Concrete is a hard composite of calcium sulfate, calcium aluminate, calcium silicate, lime, grit, and aggregates such as crushed rock and sand. Water is mixed with the concrete to form a slurry. Often the slurry has very poor flow properties. To alleviate this, additives are included in the slurry to improve flow and to adjust surface tension. Such additives are commonly called plasticizers, super plasticizers, or surfactants.
In a concrete formulation, the calcium substances react with water to form a cured, solid material. The cured concrete often has little flex to it. High molecular weight polymers may be added to concrete formulations to improve the flexibility of the cured concrete. Such polymer-modified concrete is often used in airport runways. The pounding of heavy aircraft landing can crack normal concrete due to the inflexible nature of the substance. However, with polymer additives the concrete flexes and gives the runway greater longevity.
There are many problems with current polymeric concrete additives. Generally, the additives used are not environmentally friendly (i.e. “green”) and may release toxic substances. For example, the concrete additive polyacrylamide is not biodegradable and persists in the environment. In addition, the acrylamide monomer is liberated from the polymer. The acrylamide monomer is a suspected carcinogen and has encountered increasing regulations. Polyacrylamide is further plagued by the fact that the nitrogen and carbonyl can chelate metals. The ionic strength of a mixture thus greatly impacts polyacrylamide, as polyacrylamide is capable of absorbing up to 1000 times its weight in distilled water, yet absorbs only 50 times its weight in 3% saline solution. Concrete plasticizers and surfactants are often based upon ethylene glycol, which may be released as a toxic material upon degradation. Current concrete polymers may also release their monomer constituents, which can act as neurotoxins, mutagens, teratogens, and can harm human and animal reproductive systems.